The general packet radio service (GPRS) is a packet oriented mobile data service for cellular communications systems, such as the global system for mobile communications (GSM), wideband code division multiple access (WCDMA), long term evolution (LTE) and wireless local area network (WLAN). A general packet radio system (GPRS) tunneling protocol user (GTP-U) node supports one or more GTP-U endpoints. Each pair of GTP-U endpoints is known as a GTP-U path which carries multiple GTP-U tunnels. GTP-U tunnels carry GTP-U data packets (also known as G-PDUs) between a pair of GTP-U tunnel endpoints. A tunnel endpoint is identified by a tunnel identifier, e.g., tunnel endpoint identifier (TEID).
A TEID identifies a unicast or multicast GTP-U tunnel endpoint in the receiving GTP-U node for a given GTP-U endpoint. The TEID is included in the GTP header of the G-PDU. The receiving end of a unicast GPRS tunneling protocol, GTP, tunnel assigns the TEID value that the transmitting end should use. The transmitting end of a multicast GTP tunnel assigns the TEID value the receiving end should use. The TEID values are exchanged between tunnel endpoints using control plane messaging.
The control plane procedures to setup a GTP-U tunnel are defined in protocols such as GTP-C, Radio Access Network Application Part (RANAP), S1-Application Protocol (S1-AP), X2 Application Protocol (X2-AP) and M3 Application Protocol (M3AP).
FIGS. 1 and 2 show a known GPRS 10 which includes three GTP-U nodes 12a, 12b and 12c (referred to collectively herein as “GTP-U nodes 12”) that are connected by an Internet Protocol (IP) network 18. Each GTP-U node acts as a sender and a receiver of G-PDUs. FIG. 1 shows a unicast G-PDU being sent between GTP-U nodes 12c and 12a. FIG. 2 shows the same known GPRS 10 with the three GTP-U nodes 12a, 12b and 12c connected by the Internet network 18. In FIG. 2, a multicast G-PDU is being sent from GTP-U node 12a to GTP-U node 12b and to GTP-U node 12c. 
Active IP probe based sampling of the IP path carrying the GTP-U tunneled traffic is currently used as a methodology for estimating the end-to-end state and performance of the unicast subscriber connection across the IP network. However, active IP probe based sampling does not measure the actual packet delay, packet delay variation and packet loss encountered by the user traffic carried on unicast GTP-U tunnels. The same problem exists for multicast GTP-U tunnels. Active IP probe based sampling, like the One-Way Active Measurement Protocol (OWAMP) and Two-Way Active Measurement Protocol (TWAMP), only provide a rough estimate of the performance perceived by the aggregated set of GTP-U tunnels on a given path.
The Internet engineering task force (IETF) standard body has defined an IP flow information export (IPFIX) architecture and protocol for selective monitoring of IP flows passing through an observation point and the export of measured IP flow information. IPFIX does not address the selective monitoring of GTP-U tunnels. IP flow information export does not provide the required granularity and depth of information to properly monitor the performance of a specific GTP-U tunnel. Furthermore, IPFIX is not designed to provide path performance statistics like end-to-end packet delay and packet loss. Such statistics are useful for characterizing tunnel performance.